Slide valve pump

ABSTRACT

A cylindrical piston fixed to the lower end of a cylindrical rod and a second tubular piston slideably carried over the rod. The pistons and a portion of the rod are disposed within the bore of a tubular housing. The housing includes inlet and outlet ports adjacent to its lower and upper ends, respectively, which extend from the bore through the housing wall. Reciprocating movement of the rod through the bore causes the fixed and tubular pistons to cyclically seal and unseal the inlet and outlet ports respectively whereby fluid is drawn into the inlet ports and expelled through the outlet ports.

United States Patent Spears [54] SLIDE VALVE PUMP [72] Inventor: Harry L. Spears, 10919 Sageriver Drive, Houston, Tex. 77034 [22] Filed: Aug. 14, 1969 [21] Appl. No.: 850,201

[52] US. Cl. ..417/498, 417/430, 417/501 [51] Int. Cl. ..F04b 7/04, F04b 39/ 10 [58] Field of Search ..417/430, 478, 488, 489, 490,

Welling ..417/498 X [451 Oct. 10, 1972 FOREIGN PATENTS OR APPLICATIONS 800,472 8/ 1958 Great Britain ..417/501 Primary Examiner-Carlton R. Croyle Assistant ExaminerRichard E. Gluck Att0rney-Carlos A. Torres ABSTRACT A cylindrical piston fixed to the lower end of a cylindrical rod and a second tubular piston slideably carried over the rod. The pistons and a portion of the rod are disposed within the bore of a tubular housing. The housing includes inlet and outlet ports adjacent to its lower and upper ends, respectively, which extend from the bore through the housing wall. Reciprocating movement of the rod through the bore causes the fixed and tubular pistons to cyclically seal and unseal the inlet and outlet ports respectively whereby fluid is drawn into the inlet ports and expelled through the outlet ports.

9 5 Drawing. a!

P'A'TENTEflocnom'r: 3,697,199

' SHEETIOFZ Harry L. Spears INVENTOR BY QIMRTW ATTORNEY PATENTEDum 10 m2 SHEET 2 OF 2 FIG. 5

A TTORNEY sum: VALVE PUMP BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to means for moving fluids from one location to another. More specifically, the present invention relates to a pump for elevating fluids and, in particular, to a pump for raising subterranean petroleum fluids through production tubing in completed oil wells.

2. Description of the Prior Art A conventional oil well includes a cased well bore with one or more strings of tubing extending downwardly through the casing into the oil or other petroleum fluid contained inthe subsurface mineral formation to be produced. The casing is perforated at the level of the production zone to permit fluid flow from the formation into the casing, and the lower end of the tubing string is generally open to provide entry for the fluid in the casing.

One type of pump conventionally employed in structures of the type described is wedged into an internal constriction or seating nipple formed internally of the tubing below the fluid level. A metallic enlargement on the external body, of the pump prevents it form travelling below-the seating nipple and resilient seal rings on the body of the pump'housing act to form a leakproof seal between the seating nipple and pump. The pump is generally driven by a mechanical linkage of metal rods, referred to in the trade as sucker rods which extend from the pump to the well surface. The sucker rod linkage is powered in a reciprocating motion by a conventional mechanical apparatus usually called a pumping unit located at the well surface.

The conventional pump itself generally includes. a housing through which a piston is reciprocated by the sucker rod linkage. In its simplest form, the conventional pump of the type described often includes a number of ball and seat valves with one such valve in the piston and another at the inlet port of the housing. On the upstroke of theplunger, the ball in the inlet port valve is drawn away from its seat and the ball of the outlet port valve is forced over its seat to draw fluid from below the sealing nipple and into the housing. On the pistons downstroke, the ball in the inlet valve is forced onto its seat and the ball in the piston valve moves away from its seat to allow the piston to move downwardly through the fluid contained in the housing. On the subsequent upstroke, the closing of the piston valve forces the fluid above the piston out of the housing through the outlet ports and into the tubing above the sealing nipple and simultaneously fills the housing below the piston with fluid. Repetition of this cycle eventually fills the tubing string and causes the fluid to flow to the surface.

The previously described pump or some variation thereof is probably the most widely employed in applications where it is desired to drive a subsurface pump by a surface powered, mechanical linkage. One of the most significant problems in pumps of this type is caused by wear of the ball and seat valves. The fluid produced from many formations contains minute, abrasive particles such as sand which lodge between the ball and the seat and wear away the valve components. Over a period of time, the sealing efficiency of the valves is reduced to such an extent that the pump must be removed and repaired or replaced; in some wells, where the production fluid is particularly sandy or corrosive, pumps of the type described must be replaced at frequent intervals. It is, of course, evident that removing and repairing or replacing a pump, and the associated losses caused by reduced production time can be significant expense factors.

Yet another loss in conventional pumps is associated with the reduction in fluid output caused by the faulty seating of the valves during their periods ofproduction. Thus, in some cases, it may be more economical to continue to operate the pump at a reduced efliciency caused by valve wear rather than to have the pump removed and repaired.

Ball valve pumps are also relatively limited in theoretical efiiciency and cycling rate due to their inherent principle of operation. Any increase in the amount of fluid which can be produced by such a pump usually involves an increase in the driving power and pump dimensions and includes a corresponding decrease in efficiency. Moreover, the valve closure time required for the ball and seat type valves restricts the speed of the pumping cycle and thereby further limits the maximum production rate of pumps employing these valves.

SUMMARY OF THE INVENTION The pump of the present invention employs sliding pistons as a valving mechanism rather than the conventional ball and seat arrangement. In the pump of the present invention, a small clearance is provided between pistons and bores and is filled with the fluid being pumped to produce an effective seal between the two components. The clearance between the piston and the pump bore eliminates metal-to-metal contact and thereby reduces valve wear and resultant leakage.

In its broadest aspect, the pump of the present invention employs a first piston which is directly moved by an external power source and a slave piston which is moved by the resultant pressure differentials created by the movement of the first piston. In one embodiment, where the pump is to be employed in a conventional oil well structure, the first or lower piston is fixed to the lower end of a cylindrical rod and the upper piston, which has a tubular form, is adapted to slide over the rod. O-rings are carried internally of the upper piston to form a sliding seal with the rod. The two pistons and a portion of the rod are carried in the bore of a tubular housing where the reciprocating axial movement of the rod produces a similar movement in the lower piston. The upper piston is, however, free to slide over the rod and its axial movement is controlled by the resulting pressure differentials created across its length. These pressure differentials act to move the upper piston to appropriately open or close the outlet ports of the pump which in turn permits fluid to be expelled through the outlet ports and prevents return flow into the pump.

The bore of the pump housing is provided with internal restrictions which limit the axial movement of the upper piston whereby a low pressure area is created between the two pistons as the axial distance between them increases during the downstroke of the lower piston. When the lower piston has moved below the inlet ports, fluid is forced through the inlet ports to fill the low pressure area. The operation of the pump thereby effects a positive flow into the pump bore which in turn permits an increase in the pumping rate.

The design of the pump also produces a continuous fluid flow over the operating surfaces of the pump to lubricate and prevent any particle buildup. As a result, the pump operates more smoothly and wear is reduced.

The lower end of the pump is equipped with a pump guide having a pointed, external contour to prevent premature lodging of the pump as it is lowered through the tubing and into the seating nipple. The pump guide and the upper portion of the pump assembly are also provided with ports which communicate with the housing bore to prevent a fluid lock and to form a pathway for the lubricating and washing action of the fluid.

The pump of the present invention is durable and capable of efficiently producing more volume than is presently possible with conventional ball and seat type pumps with the same power input. The design of the pump produces a smoothness of operation which reduces sucker-rod breakage often associated with conventional pumps, increases efficiency and reduces the cost of manufacturing the pump.

LEF QESQRLBTIQHQE.TMAXQIQS.

FIG. 1 is a partial elevation, partially in section illustrating a standard oil well structure equipped with the preferred form of the pump of the present invention;

FIG. 2 is an elevation, partially in section illustrating the pump of FIG. 1 at the bottom of its stroke;

FIG. 3 is an elevation, partially in section illustrating the pump of FIG. 1 at the mid-point of its upstroke;

FIG. 4 is an elevation, partially in section, illustrating the pump of FIG. 1 at the top of its stroke;

FIG. 5 is an elevation, in section, illustrating a second form of the pump of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.-. V

With reference to FIG. 1 of the drawings, the pump of the present invention, designated generally at 10, is disposed in a conventional well structure which includes a string of casing C. The casing C is perforated to permit petroleum fluid P to flow into the casing from a subsurface formation F.

A second conduit string T, generally referred to as tubing, extends through the casing C and into the petroleum fluid P in the casing. The tubing T is provided with an internal restriction or seating nipple, indicated generally at N, which forms a seal with and supports the pump 10.

As with conventional pumps, the pump is driven by a reciprocating linkage S of sucker rods to raise fluid from below the seating nipple N and expel it into the tubing T above the nipple. This pumping action eventually fills the tubing T and forces fluid through a production line L at the well surface.

Details in the construction of the pump 10 of the present invention may best be described by reference to FIG. 2 of the drawings. The pump 10 includes a first lower, cylindrical piston 11 threadedly secured to a cylindrical rod 12. The upper end of the rod 12 is threadedly secured to the lower end of the sucker-rod linkage S. A second tubular piston 13 is carried about the rod 12 between the piston 11 and sucker-rod linkage S and is free to move axially with respect to the rod.

An O-ring bushing 13a is threadedly secured within the upper end of the piston 13 and carries two resilient 0- rings 13b which form a sliding'seal between the piston 13 and the rod 12. A plural part housing indicated generally at 14 surrounds the pistons 11 and 13 and a portion of the rod 12. The housing 14 includes an upper housing section 140, a hold-down body 14b, and a lower housing section 14c. Threads formed on the upper and lower housing sections 14a and 14c respectively are firmly engaged with cooperating threads formed at either end of the hold-down body 14b as illustrated in the drawings.

The hold-down body 14b includes a radially enlarged box section 14b extending outwardly from a smaller shank portion 14b". The external dimensions of the section 14b are greater than the internal dimensions of the seating nipple N which prevents the pump 10 from moving below the seating nipple in the tubing string T. The external dimensions of the pump 10 below the section 14b are less than the internal dimensions of the seating nipple N which thereby permits the lower portions of the pump 10 to extend below the seating nipple as illustrated in FIG. 1 of the drawings.

The shank 14b" of the hold-down body 14b supports a conventional sealing assembly which includes a plurality of resilient seating cups 15 axially spaced from each other by spacers 16. The seating cups l5 and spacers 16 are fixed against axial movement with respect to the hold-down body 14b by means of a jam nut 17 which engages threads on the shank 14b" to hold the sealing assembly securely against the enlarged section 14b. As best illustrated in FIG. 1, the seating cups form a leak-proof seal between the pump 10 and the seating nipple N which isolates the internal tubing area above the nipple N from the area below the nipple.

A composite central bore extends through the housing 14 and is formed by the internal cylindrical surfaces 14d, 14s, and 14f of the housing sections 14a, 14b, and respectively. The axial length of the bore surface 14f is substantially greater than that of the bore surface 14d since the axial distance travelled by the piston 1 l is greater than that travelled by the piston 13. A rod guide 18 is threadedly engaged with internal threads formed in the upper end of the housing section 14a for restricting lateral movement of the rod 12. The lower axial end of the rod guide 18 also acts to limit the upward axial movement of the piston 13. At the lower end of the housing 14, a pump guide 19 is threadedly engaged with internal threads formed in the lower end of the housing section 14c and is employed primarily for preventing the pump from prematurely lodging as it is being lowered through the tubing T and into the seating nipple N.

A small clearance 20 is provided between the outer surface of the piston 11 and the bore surface 14f with a similar clearance 21 provided between the piston 13 and and the bore surface 14d. When the pump 10 is submerged, clearances 20 and 21 are filled with the fluid being pumped which produces an effective seal between the pistons and the bore surfaces. The two clearances also provide lubrication of the housing bore surfaces and pistons to reduce wear and add to the smoothness of operation of the pump.

A series of inlet ports 14g are provided about the circumferences of the lower housing section 14c for admitting fluid below the seating nipple N into the housing bore. The pump guide 19 is provided with an axial bore 19a which intersects four radial circulating ports 19b. When the lower end of the piston 11 is below the bottom of the inlet ports 14g during any portion of the pumping cycle, the bore 190 and ports 19b provide a flow path to prevent fluid lock of the piston 11. The resultant fluid movement through the bore 19a and ports 19b also creates a washing action which prevents any accumulation of particles in the pump and lubricates the lower portion of the bore surface 14f.

A series of outlet ports 14h are provided about the circumference of the upper housing section 14a for exhausting fluid from the housing bore and into the tubing string T above the seating nipple N. Immediately above the outlet ports 14h, a series of circulation ports l4i is also provided about the circumference of the housing section 14a. The ports l4i cooperate with four circulating ports 18a which extend through the rod guide 18 to provide a pathway for fluid contained within the bore housing above the piston 13. The resultant fluid flow through the ports 14i and 18a acts to prevent the piston 13 from being fluid locked and to lubricate the upper portion of the bore surface 14d as well as to prevent any particle build-up in andabout the P p t In the initial installation of the pump 10 of the present invention in a conventional oil well structure, the pump is lowered through the tubing string T until the enlarged section 14b of the hold-down body 14b engages the restriction formed by the seating nipple N. During the descent through the tubing string T, the external contour of the pump guide 19 assists in directing the pump past tubing deviations and obstacles formed internally of the tubing and thereby prevents the pump 10 from prematurely lodging before it is properly positioned in the seating nipple. With the pump 10 positioned in the seating nipple N as illustrated in FIG. 1, the resilient seating cups form a leakproof seal which isolates the area below the seating nipple from the internal area of the tubing T above the nipple.

With the initial positioning of the pump being thus described, the operation of the pump 10 may best be understood by reference to FIGS. 2-4 which illustrate the pump structure at various phases of the stroke. With initial reference to FIG. 2, the pistons 11 and 13 are illustrated at the bottom of the pumping stroke. In this position, the lower piston l 1 is below the inlet ports 14g which permits fluid in the tubing T below the nipple N to flow into and fill the housing bore in the area between the two pistons 11 and 13. The upper piston 13 simultaneously covers the outlet ports 14!: to prevent the fluid in the tubing T above the seating nipple N from flowing into the housing bore. It will be understood that the sliding seal formed by the O-rings 13b prevents any fluid flow between the rod 12 and the piston 13 whereby the fluid in the tubing T above the nipple N is completely sealed away from the internal housing area between the two pistons 1 l and 13.

As best illustrated with reference to FIG. 2, when the sucker-rod linkage S and attached rod 12 begin the upstroke ofthe pumping cycle, the piston 11 is pulled upwardly, and after a short length of travel, closes over and seals the inlet ports 143 to trap the fluid contained within the housing bore between the two pistons. Continued upward movement of the piston 11 lifts the fluid trapped in the housing bore and the fluid in turn transmits this lifting force to the upper piston causing it to move upwardly through the housing bore until it engages the lower end of the rod guide 18. The sliding seal formed by the 0-rings 131; permits the rod 12 to continue to move upwardly through the stationary piston 13. When the bottom of the upper piston 13 has thus been raised above the outlet ports 14h, and is in the position illustrated in FIG. 3 the outlet ports are thereby opened and the fluid in the housing bore is forced out through the outlet ports by continued upward movement of the piston 11 as it completes its upstroke.

After the piston 11 reaches the top of its upstroke, as illustrated in FIG. 4, the movement of the sucker-rod linkage S cycles and begins to drive the piston 11 downwardly through the downstroke. The downward movement of the piston 1 1 produces an initial lowering of pressure in the housing bore between the two pistons and thereby creates a resultant force which immediately moves the piston 13 downwardly to close the outlet ports 14h. An internal restriction formed by the upper axial end of the hold-down body 14b prevents the piston 13 from moving below the outlet ports 14h and holds the piston 13 in position for the next upstroke.

As the rod 12 continues to move downwardly through the sliding seal in the stationary piston 13, an increasing low pressure area is created in the housing bore between the two pistons as they move further apart. When the top of the lower piston l 1 has moved below the top of the inlet ports 14g, fluid rushes into the inlet ports to fill the housing bore in the low pressure area between the two pistons. The driving force transmitted through the sucker-rod linkage S then reverses and the pumping cycle is repeated.

FIG. 5 of the drawings illustrates a second form of the pump of the present invention indicated generally at 100. The reference characters employed in FIG. 5 are 10 times the value of the characters employed in identifying corresponding features of the form of the pump illustrated in FIGS. l-4. The embodiment of FIG. 5 is adapted to be driven by a rod which extends into the bottom of the pump housing 140. Circulating ports 180a extend through the rod guide 180 to act as relief ports for fluid trapped below the lower piston 110. The upper piston has a solid cross sectional area, and its axial motion is directly governed by I the pressure differentials existing within the bore of the housing 140. The top of the housing is capped by a fitting 210 which is provided with circulating ports 210a. The ports 210a serve essentially the same purpose as the ports 18a in the embodiment of FIGS. l-4.

The operation of the embodiment of the present invention illustrated in FIG. 5 corresponds to that previously described with reference to the form illustrated in FIGS. l-4. It will, of course, be understood that any suitable means (not shown) may be provided-for driving the rod 120 through the required reciprocating axial movement.

While the pump of the present invention has been described as being particularly suited for use in oil well structures, it will be understood that the pump is of general utility wherever it is required that fluids of any type be transported from one place to another. Thus,

by way of example rather than limitation, the pump may be employed in a water well or in driving fluids through a horizontal pipe line. In any of its applications, it will be understood that the power source may be a conventional reciprocating sucker-rod linkage where suitable, or it may be some other device or mechanism for imparting reciprocating motion to the rod 12 or 120. It will also be appreciated that the structure of the pump may be modified without departing from the present invention. As an example, the sealing assembly described for positioning and sealing the pump in a seating nipple may take on various conventional forms, and in some applications may be completely unnecessary. In the way of further example, the pistons 11 and 13, which has been illustrated and described as being tubular or cylindrical in form, may in fact assume various other forms. It will also be understood that even though the two pistons have been illustrated as having approximately the same lateral and axial dimensions, they may in fact have differing dimensions provided they appropriately conform to the internal dimensions of the respective portions of the housing bore. In suitable applications, the pistons 11 and/or 13 may also employ annular gaskets or O-rings or other suitable means for forming a friction seal with the internal surfaces of the housing bore.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and various changes in the size, shape and materials as well as in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention.

Iclaim:

l. A fluid pump comprising:

a. housing means having first and second axially spaced ends;

b. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively;

c. piston lifting means disposed within said housing means and movable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means;

d. drive means secured to said lifting means for moving said lifting means axially through said housing means;

e. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means;

f. a closed bore section extending axially between the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore;

g. an axially extending opening formed between said first and second ends of said valving means;

h. an elongate rod means included in said driving means, extending into said first housing means end and through said valving means opening and being axially movable with respect to said valving means;

. sealing means included between said valving means and rod means for forming a sliding seal between said valving means and said rod means;

. said valving means including a substantially tubular valve body having an axially extending cylindrical outer surface formed along at least a portion of said valve body;

k. first and second axially spaced restricting means included in said housing means for limiting the axial travel of said valve body in said housing means;

. said lifting means including a piston body having first and second axially spaced ends and a substantially cylindrical outer surface formed along at least a portion of said piston body;

m. third and fourth restricting means included in said housing means for limiting the axial travel of said piston body in said piston bore;

11. said inlet means including inlet port means extend-.

ing through said housing means between said third and fourth restricting means;

said third restricting means disposed axially between said inlet port means and said first housing means end; and

p. said cylindrical piston surface movable axially said second restricting means is positioned axially between said outlet port means and said second housing end; and

. said cylindrical outer surface on said valve body is closely surrounded by a valve bore in said housing means and is moveable axially in said valve bore between said outlet port means and said first restricting means to an axial location where said outlet port means is non-coincident with said cylindrical valve body surface for permitting fluid to flow out of said housing means through said outlet port means.

. A fluid pump comprising:

housing means having first and second axially spaced ends;

. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively;

. piston lifting means disposed within said housing means and movable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means;

. drive means secured to said lifting means for moving said lifting means axially through said housing means;

. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said bore to open and close said outlet means;

f. a closed bore section extending axially between the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore;

g. first circulating means adjacent said first housing means end for moving fluid into and out of said housing means as said valving means is moved; and

h. lower openings included in said first circulating means extending through said housing means into said valve bore adjacent and above the uppermost sealing point of said valve bore and valving means when said valving means is at its lowermost point in said valve bore whereby fluid and solid particles may flow into and out of said valve bore at axially spaced locations for preventing particle buildup in said valve bore.

4. The fluid pump as defined in claim 3 further including second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppennost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore. v r i I 5. A fluid pump comprising:

a. housing means having first and second axially spaced ends; axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively;

c. piston lifting means disposed within said housing means and movable axially through a piston bore in saidhousing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means;

. drive means secured to said lifting means for moving said lifting means axially through said housing means;

e. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means;

f. a closed bore section extending axially between the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore; and

g. second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppermost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore.

6. A fluid pump comprising:

a. housing means having first and second axially spaced ends;

axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively;

c. piston lifting means disposed within said housing means and moveable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means;

d. drive means secured to said lifting means for moving said lifting means axially through said housing means;

e. valving means having first and second axially spaced ends disposed within said housing means and a moveable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means;

f. first circulating means adjacent said first housing means end for moving fluid into and out of said housing means as said valving means is moved; and

g. lower openings included in said first circulating means extending through said housing means into said valve bore adjacent and above the uppermost sealing point of said valve bore and valving means when said valving means is at its lowermost point in said valve bore whereby fluid and solid particles may flow into and out of said valve bore at axially spaced locations for preventing particle buildup in said valve bore.

7. A fluid,pump as defined in claim 6 further including second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppermost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore.

##tta 

1. A fluid pump comprising: a. housing means having first and second axially spaced ends; b. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively; c. piston lifting means disposed within said housing means and movable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means; d. drive means secured to said lifting means for moving said lifting means axially through said housing means; e. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means; f. a closed bore section extending axially between the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore; g. an axially extending opening formed between said first and second ends of said valving means; h. an elongate rod means included in said driving means, extending into said first housing means end and through said valving means opening and being axially movable with respect to said valving means; i. sealing means included between said valving means and rod means for forming a sliding seal between said valving means and said rod means; j. said valving means including a substantially tubular valve body having an axially extending cylindrical outer surface formed along at least a portion of said valve body; k. first and second axially spaced restricting means included in said housing means for limiting the axial travel of said valve body in said housing means; l. said lifting means including a piston body having first and second axially spaced ends and a substantially cylindrical outer surface formed along at least a portion of said piston body; m. third and fourth restricting means included in said housing means for limiting the axial travel of said piston body in said piston bore; n. said inlet means including inlet port means extending through said housing means between said third and fourth restricting means; o. said third restricting means disposed axially between said inlet port means and said first housing means end; and p. said cylindrical piston surface movable axially between said inlet port means and said fourth restricting means to an axial location where said inlet port means is non-coincident with said cylindrical piston surface for permitting fluid to flow into said piston bore through said inlet port means.
 2. The fluid pump as defined in claim 1 wherein: a. said outlet means include outlet port means extending through said housing means axially between said first and second restricting means; b. said second restricting means is positioned axially between said outlet port means and said second housing end; and c. said cylindrical outer surface on said valve body is closely surrounded by a valve bore in said housing means and is moveable axially in said valve bore between said outlet port means and said first restricting means to an axial location where said outlet port means is non-coincident with said cylindrical valve body surface for permitting fluid to flow out of said housing means through said outlet port means.
 3. A fluid pump comprising: a. housing means having first and second axially spaced ends; b. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively; c. piston lifting means disposed within said housing means and movable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means; d. drive means secured to said lifting means for moving said lifting means axially through said housing means; e. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said bore to open and close said outlet means; f. a closed bore section extending axially betweeN the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore; g. first circulating means adjacent said first housing means end for moving fluid into and out of said housing means as said valving means is moved; and h. lower openings included in said first circulating means extending through said housing means into said valve bore adjacent and above the uppermost sealing point of said valve bore and valving means when said valving means is at its lowermost point in said valve bore whereby fluid and solid particles may flow into and out of said valve bore at axially spaced locations for preventing particle buildup in said valve bore.
 4. The fluid pump as defined in claim 3 further including second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppermost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore.
 5. A fluid pump comprising: a. housing means having first and second axially spaced ends; b. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively; c. piston lifting means disposed within said housing means and movable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means; d. drive means secured to said lifting means for moving said lifting means axially through said housing means; e. valving means having first and second axially spaced ends disposed within said housing means and movable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means; f. a closed bore section extending axially between the axially uppermost opening in said inlet means and the axially lowermost sealing point of said valve bore and valving means when said valving means is at the lowest axial point in said valve bore; and g. second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppermost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore.
 6. A fluid pump comprising: a. housing means having first and second axially spaced ends; b. axially spaced outlet and inlet means opening into said housing means adjacent said first and second housing means ends respectively; c. piston lifting means disposed within said housing means and moveable axially through a piston bore in said housing means to form a sliding seal with a portion of said piston bore for moving fluid into said housing means through said inlet means and out of said housing means through said outlet means; d. drive means secured to said lifting means for moving said lifting means axially through said housing means; e. valving means having first and second axially spaced ends disposed within said housing means and a moveable axially within a valve bore in said housing means to form a sliding seal with a portion of said valve bore to open and close said outlet means; f. first circulating means adjacent said first housing means end for moving fluId into and out of said housing means as said valving means is moved; and g. lower openings included in said first circulating means extending through said housing means into said valve bore adjacent and above the uppermost sealing point of said valve bore and valving means when said valving means is at its lowermost point in said valve bore whereby fluid and solid particles may flow into and out of said valve bore at axially spaced locations for preventing particle buildup in said valve bore.
 7. A fluid pump as defined in claim 6 further including second circulating means adjacent said second housing means end for moving fluid into and out of said housing means as said lifting means is moved with said inlet means being adjacent and below the lowermost sealing point between said piston means and said piston bore when said piston means is at its uppermost point in said piston bore whereby fluid and solid particles may flow into and out of said piston bore at axially spaced housing locations to prevent particle buildup in said piston bore. 